Viscosity of dilute suspensions of weakly flocculated Na-montmorillonite under low pressure gradient

The clay mineral montmorillonite has considerable potential as a pollutant adsorption material, and understanding its unique rheological behaviors is important for realizing environmental applications. In this study, the viscosity of dilute suspensions of montmorillonite under the conditions of extremely low pressure gradients was measured using a homemade spiral-type capillary viscometer in order to understand macroscopic flow properties in terms of microscopic colloidal interactions. Experiments were conducted at neutral pH with background NaCl concentration ranging from 5.0 × 10−3 to 5.0 × 10−2 M wherein edge–face interactions between clay sheets are expected to dominate. We have determined the intrinsic viscosity K1 and Huggins parameter K2/K12 to analyze the effects of two-body interactions and the non-Newtonian behaviors of clay suspensions. K1 was 1.0 × 103–1.5 × 103, which is considerably larger than that reported for pH 10 with the same ionic strength. Moreover, when non-Newtonian behavior was detected, Huggins parameter was >1.